Needles are devices manufactured to pass through skin, and typically formed of metal with proven strength and biological safety. As illustrated in FIG. 1, a conventional acupuncture needle has a needle point, a needle body and a needle handle, and is formed of materials such as stone, gold, silver, copper, iron, bone, thorns, etc. In recent years, with the development of technology, stainless steel 304 or 316L and the like is being used as a material of a needle, which is sturdy, not easily broken, resistant to corrosion and harmless to a human body.
Since pain felt by a patient upon insertion of a needle varies according to the thickness and surface condition of a commonly used injection needle, many conventional technologies have been developed in a direction of reducing the degree of pain of the patient. For example, a silicone layer is applied onto a needle surface as a method for reducing friction between the needle and human tissue upon insertion of a needle, or a needle surface is processed to be smooth to decrease surface roughness to reduce resistance generated upon insertion of a needle, thereby reducing pain felt by a patient. Furthermore, as the thickness of the needle becomes thinner, a smaller amount of pain of the patient is generated upon insertion of the needle, and thus thinner needles are increasingly being manufactured and used.
The purpose of use of an injection needle (needle for injection) is to inject a certain drug into body tissues such as blood vessels, muscles or the like through the injection needle, while a direct therapeutic effect is not expected by insertion of an injection needle itself. However, an acupuncture needle intends to achieve a therapeutic effect by inserting a needle into specific areas such as meridians, acupoints or the like without the purpose of injection of a drug. Consequently, there is a fundamental difference in the purpose of injecting a needle between them.
That is, physical stimulation of body tissues by a needle upon insertion of the needle is considered important for an acupuncture needle, unlike an injection needle. However, regardless of a therapeutic effect of a needle, an acupuncture needle is produced using a similar method as that of a typical injection needle for the purpose of reduction in pain felt by a patient upon insertion of a needle. Furthermore, pain felt by a patient can be reduced according to a state of a needle surface, but there are no experimental results showing that the therapeutic effect of the needle is the same.
Conversely, according to research on a needle and tissue (H. Langevin, 2002, Faseb), a result has been reported showing that connective tissue is wound around a needle surface by turning a needle from side to side after the needle is inserted, and stimulation thus obtained exhibits the therapeutic effect of the needle. This experiment result indicates that a binding force between a needle surface and connective tissue is important to the therapeutic effect of the needle. In other words, it means that when the binding force between them is increased by changing physical properties of a needle surface, the therapeutic effect of the needle can be improved. However, technologies for reducing roughness of a needle surface has been utilized in production of an acupuncture needle until now, which indicates that research has been conducted in a direction of decreasing the binding force between them.
Further, a technology for changing physical properties of a needle surface commonly used in production of a needle is to apply a chemical material on a needle surface. An objective of this technology is largely divided into two types in accordance with a material to be applied, and there are the case where a material such as silicone or the like is applied for the purpose of lubrication and the case where a material such as salicylic acid is applied for antibacterial and therapeutic purposes. However, needles produced by these technologies have a problem of a reduced binding force between a needle surface and connective tissue.
Moreover, a material mainly used for typical injection needles and acupuncture needles is stainless steel, and SS304 and SS0316L are the most frequently used stainless steels, both of which belong to the austenitic stainless steels. One of the methods for reducing surface roughness of these stainless steels is electropolishing, which is a technology frequently used for SS304 and SS0316L in particular. Electropolishing is a technology in which when electricity is applied to a metal to be polished in an electrolyte, an initial oxidation layer with viscosity is formed on the metal due to electrolysis to form a passivation film of the metal oxide, and thereby a relatively bent and protruded surface is more shaved to have the whole surface of the metal flattened. By applying this technology, the surface roughness of the stainless steel is adjusted.
Another technology is to process a surface using a strong laser (laser ablation), which is a method of instantaneously ablating a surface material by allowing a strong laser pulse beam incident to a metal to form a pattern. At this time, the depth of the pattern can be adjusted by controlling an output of a laser. Currently, this technology is utilized not only for a metal, but also for marking the silicon wafer for manufacturing a semiconductor. Furthermore, the most frequently used method for surface-treating an acupuncture needle is mechanical grinding, which has been developed in a direction of forming a needle point and reducing surface roughness. However, it is difficult to form a surface with a directional characteristic by this technology.
Korean Laid-Open Patent Publication No. 2008-0112759 discloses a technology of preparing an acupuncture needle where an effective area of a needle surface brought in contact with connective tissue is enlarged by physically changing the needle surface to increase a binding force between them, but there is a problem of skin damage due to roughness of a needle surface.